Travelling wave electron discharge tubes



March 20, 1962 T. H. STAERCK 3,026,445

TRAVELLING WAVE ELECTRON DISCHARGE TUBES Filed March 9, 1959 W1 19 K/ WUnited States Patent 3,026,445 TRAVELLING WAVE ELECTRON DISCHARGE TUBESThomas Henry Staerck, Hornchurch, England, assignor to English ElectricValve Company, London, England, a British company Filed Mar. 9, 1959,Ser. No. 798,211 Claims priority application Great Britain Mar. 18, 19583 Claims. (Cl. SIS-3.5)

This invention relates to travelling wave electron discharge tubes andmore specifically to such tubes of the kind in which an electron beam isprojected axially down a delay winding which is coupled thereto. Suchtravelling wave tubes are now well known and in fairly common use formicrowave amplification and other purposes.

As is well known, if a travelling wave tube of the kind referred to isto give high performance at microwave frequencies, it is necessary thatthe delay winding shall be precisely located in a mechanically stablemanner with respect to the electron beam to which it is coupled, andVarious proposals have been made to satisfy this requirement which inpractice is by no means easy to satisfy in an economical manner. Forexample, it is known to support the delay winding, which is usually ahelix, by means of a plurality of (for example three) insulating supportrods which extend parallel to the axis and contact with the periphery ofthe winding along lines equally spaced around said periphery, and tohold the rods with gentle but firm pressure against the winding by meansof specially formed clamps encircling the plurality of rods at spacedpoints in their lengths. This type of construction has the defect thatthe clamps are troublesome to make and fit and even so are not alwayswholly satisfactory, since they provide clamping only at intervals alongthe lengths of the support rods. Another known expedient for fixing thedelay winding in position in a stable manner consists of pre-glazing thesupport rods, assembling them with the winding in a jig, and applyingheat treatment to cause the glaze to flow in such a manner as to stickthe turns of the winding to the rods. This proposal is expensive tocarry out and, moreover, may result in inacceptably increased radiofrequency losses due to the glaze.

The object of the present invention is to provide simple and economicalconstructions for accurately locating the delay winding of a travellingwave tube of the kind referred to without incurring the defects of theknown proposals above outlined.

According to this invention a travelling wave electron discharge tube ofthe kind having a delay winding which is co-axial with the electron beampath of the tube, is provided with a plurality of rods supporting saidwinding and in contact with the outside thereof along a plurality oflines distributed around the periphery thereof, and coiled strainedmetal spring means encircling said plurality of rods over at least asubstantial proportion of the lengths thereof, said coiled metal springmeans having, in the unstrained condition, a diameter less than that ofa cylinder which would touch the peripheries of said rods, wherebyspring force exerted by said coiled spring means presses said rodsagainst said winding.

According to a feature of this invention a travelling wave electrondischarge tube of the kind having a delay helix which is co-axial withthe electron beam path of the tube is provided with a plurality of rodssupporting said helix and in contact with the outside thereof along aplurality of lines distributed around the periphery thereof, and atleast one helically coiled strained spring in a diametrically strainedcondition encircling said plurality of rods over at least a substantialpart of the lengths thereof, whereby said metal spring, due to itsstrain, presses ice said rods against said helix. There may be a singlecoiled spring extending over the required portion of the helix length orthere may be a number of such springs, end to end or spaced apart alittle, over said length.

Preferably there are three rods at equally spaced round the periphery ofthe delay winding.

The invention is illustrated in the accompanying drawings which show, sofar as is necessary to an understanding of the said invention, atravelling wave tube of the kind referred to and embodying the saidinvention. FIG- URE 1 is a schematic elevation, broken away centrallyand at the ends, of the embodiment in question, and FIGURE 2 is asectional view at right angles to the view of FIGURE 1.

Referring to the drawings, the travelling Wave tube therein partlyrepresented has within a cylindrical envelope portion 1, shown brokenaway, a helical delay winding 2 between end members or so-called chokes3. The winding 2 co-axially surrounds the electron discharge path (notrepresented) which extends axially along inside the said winding in thecustomary manner. The winding 2 is supported by three insulating rods 4,5 and 6 spaced at 120 round the winding periphery and contacting italong three lines which are parallel to the axis. So as to simplifyFIGURE 1, the rod 6 is not shown therein, only the rods 4 and 5 beingshown. The said rods are coated with graphite or other suitableresistance material over desired portions of their lengths to provideattenuation in accordance with well known travelling wave tube practice.Such graphite coating is indicated at 7 on the rod 4 only, it being notrepresented on the other rods, again for reasons of simplifying thedrawing in FIGURE 1.

In accordance with this invention the rods 4, 5 and 6 are pressedinwardly on to the helix 2 by means of a coiled helical metal spring 8long enough to extend at least over the greater part of the length ofthe helical winding 2 and having in its unstrained condition an internaldiameter a little less than the diameter of the imaginary circlecircumscribing the rods 4, 5 and 6 and to which these rods areinternally tangential. In FIGURE 1 the spring 8 is represented as woundin the opposite direction to that of the helix 2 but of course this isnot necessary and, indeed, it is in general preferred to have the helix2 and the spring 8 wound in the same direction. To fit the coil spring8, the rods 4, 5 and 6 are placed in position and the spring 8 isunwound a little so as to increase its internal diameter sufiiciently toallow it to he slipped over the said rods 4, 5 and 6. It is thenreleased when in the required position. It will be appreciated that,when released, the spring will provide radially inward forces whichpress the rods 4, 5 and 6 inwardly against the helix 2 and position thelatter with precision and in a stable manner. It will further beobserved that the inward pressure forces applied by the spring 8 are, toa close degree of approximation, uniform over the whole length of thespring so that a very good and stable positioning and clamping action isobtained.

I claim:

1. A travelling wave electron discharge tube of the kind having a delaywinding which is co-axial with the electron beam path of the tube, saidtube including a plurality of rods which support said delay winding andare in contact with the outside thereof along a plurality of linesextending parallel to the axis and equally spaced around the peripherythereof, and coiled strained metal spring means encircling saidplurality of rods over the greater part of the length of said delaywinding, said coiled spring means having, in the unstrained condition, adiameter less than its diameter which it adopts when encircling saidrods, whereby spring force exerted by said A coiledspringmeans presses.said rods against said winding,

2. A travelling wave electron discharge tube of the kind having a delayhelix which is co-axial with the electronbeam. path' of the tube saidtube ,includingaplurality of rods supporting" said helix and in, contactwith the outside thereof along aplur'ality. of linesextending parallelto the axis. and equally spaced around the periphery thereof,- and, atleast one helically coiled strained metal spring in adiametricallystrained condition encircling said plurality of rods overthe greater part of the length of said delay helix, whereby said spring,due to its strain; presses said rods'against said helix;

3; A- tube'as' claimed in claim 1 wherein'there are 4 three straightrods spacedat 120 round the periphery of the delay winding.

References Cited in the file of this patent UNITED STATES PATENTS2,767,344 Hines Oct. 16, 1956 2,806,170 Bianculli Sept. 10, 19572,871,393 Klein et a1. n--. -h Jan. 27, 1959 2,876,379 Lauer et al. Mar.3', 1959 FOREIGN PATENTS 993,491 7 France July 25, 1951 1,152,970 FranceSept. 16, 1957 807,357 Great Britain Jan. 14, 1959

